Freestanding III-Nitride Single-Crystal Substrate and Method of Manufacturing Semiconductor Device Utilizing the Substrate

ABSTRACT

Freestanding III-nitride single-crystal substrates whose average dislocation density is not greater than 5×10 5  cm −2  and that are fracture resistant, and a method of manufacturing semiconductor devices utilizing such freestanding III-nitride single-crystal substrates are made available. The freestanding III-nitride single-crystal substrate includes one or more high-dislocation-density regions ( 20   h ), and a plurality of low-dislocation-density regions ( 20   k ) in which the dislocation density is lower than that of the high-dislocation-density regions ( 20   h ), wherein the average dislocation density is not greater than 5×10 5  cm −2 . Herein, the ratio of the dislocation density of the high-dislocation-density region(s) ( 20   h ) to the average dislocation density is sufficiently large to check the propagation of cracks in the substrate. And the semiconductor device manufacturing method utilizes the freestanding III-nitride single crystal substrate ( 20   p ).

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to freestanding III-nitride single-crystal substrates that are of low average dislocation density and are fracture resistant, and to methods of manufacturing semiconductor devices utilizing the substrates.

2. Description of the Related Art

III-nitride single-crystal substrates whose dislocation-density distribution is uniform and whose average dislocation density is low are being developed as freestanding III-nitride single-crystal substrates ideally suited to application in semiconductor devices including light-emitting devices and electronic devices.

In Japanese Unexamined Pat. App. Pub. No. 2004-193371 (Patent Document 1), for example, a freestanding substrate incorporating a III-nitride semiconductor layer of less than 1×10⁶ cm⁻² average dislocation density is disclosed—specifically, a GaN film (freestanding substrate) in which the dislocation density varies within a 0.12 to 1.5×10⁶ cm⁻² range. In Japanese Unexamined Pat. App. Pub. No. 2006-52102 (Patent Document 2), meanwhile, a III-V Group nitride system semiconductor substrate whose average dislocation density is 5×10⁷ cm⁻² or less is disclosed—specifically a GaN freestanding substrate having a dislocation-density range of 1.4±0.7×10⁶ cm⁻².

Nonetheless, freestanding III-nitride single-crystal substrates of still lower dislocation density are being sought as substrates for semiconductor devices, in order to improve semiconductor device properties further.

-   Patent Document 1: Japanese Unexamined Pat. App. Pub. No.     2004-193371 -   Patent Document 2: Japanese Unexamined Pat. App. Pub. No. 2006-52102

Accordingly, the manufacture of freestanding III-nitride single-crystal substrates of still lower dislocation density-for example, of 5×10⁵ cm⁻² average dislocation density—has been attempted. With, at an average dislocation density of 5×10⁵ cm⁻², ultra-low density freestanding III-nitride single-crystal substrates, however, those whose dislocation-density distribution is uniform have been discovered to be fracture-prone.

BRIEF SUMMARY OF THE INVENTION

Therein, an object of the present invention is to resolve the problems just discussed by making available freestanding III-nitride single-crystal substrates whose average dislocation density is not greater than 5×10⁵ cm⁻² and that are fracture resistant, and to make available a method of manufacturing semiconductor devices utilizing such freestanding III-nitride single-crystal substrates.

The present invention is a freestanding III-nitride single-crystal substrate in which the average dislocation density is not greater than 5×10⁵ cm⁻², and that includes one or more high-dislocation-density regions, and a plurality of low-dislocation-density regions in which the dislocation density is lower than that of the high-dislocation-density regions.

In a freestanding III-nitride single-crystal substrate involving the present invention, the ratio of the dislocation density of the high-dislocation-density region(s) to the average dislocation density is sufficiently large to check the propagation of cracks in the substrate. For example, it is possible to have the ratio of the dislocation density of the high dislocation density region(s) to the average dislocation density be 2 or greater. It is also possible to have the dislocation density of the high-dislocation-density region(s) be between 5×10⁵ cm⁻² and 3×10⁶ cm⁻². Likewise, it is possible to have the dislocation density of the low-dislocation-density regions be not greater than 1×10⁵ cm⁻².

Furthermore, a freestanding III-nitride single-crystal substrate involving the present invention may be one having a hexagonal crystal-system structure, and in which any chosen {1-100} plane in the substrate intersects the one or more high-dislocation-density regions. Herein, the one or more high-dislocation-density regions can be patterned in a geometry, seen from the major surface of the substrate, that includes any of striped patterns, polygonally checkered patterns, periodically arrayed islet patterns, or nonrepetitive patterns.

Still further, in a freestanding III-nitride single-crystal substrate involving the present invention, it is possible to have the surface area of the major surface be 20 cm² or greater, and to have the thickness be 1000 μm or less. It is also possible to have the freestanding III-nitride single-crystal substrate be a GaN single-crystal freestanding substrate. Yet further, the freestanding III-nitride single-crystal substrate can be formed by HVPE.

The present invention is also a method of manufacturing a semiconductor device utilizing a freestanding III-nitride single-crystal substrate as set forth above.

The present invention enables the provision of freestanding III-nitride single-crystal substrates that have an average dislocation density of not greater than 5×10⁵ cm⁻² and which are fracture resistant, and the invention can make available a method of manufacturing semiconductor devices utilizing such freestanding III-nitride single-crystal substrates.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a plan view summarily representing one example of a freestanding III-nitride single-crystal substrate involving the present invention.

FIG. 2 is a plan view summarily representing another example of a freestanding III-nitride single-crystal substrate involving the present invention.

FIG. 3 is outline sectional diagrams for illustrating one example of a method, involving the present invention, of manufacturing a freestanding III-nitride single-crystal substrate, wherein: FIG. 3A represents a process step of preparing a starting substrate; FIG. 3B represents a process step of growing III-nitride crystal onto the starting substrate by liquid-phase deposition; FIG. 3C represents a process step of growing single-crystal III-nitride onto the III-nitride crystal by vapor-phase deposition; and FIG. 3D represents a formed freestanding III-nitride single-crystal substrate.

FIG. 4 is a plan view summarily representing one example of a starting substrate employed in the manufacture of a freestanding III-nitride single-crystal substrate involving the present invention.

FIG. 5 is a sectional diagram summarily illustrating another example of a method, involving the present invention, of manufacturing a freestanding III-nitride single-crystal substrate, wherein: FIG. 5A represents a process step of forming an aggregate III-nitride crystal substrate; FIG. 5B represents a process step of growing single-crystal III-nitride onto the aggregate III-nitride crystal substrate by vapor-phase deposition; and FIG. 5C represents a formed freestanding III-nitride single-crystal substrate.

FIG. 6 is a plan view summarily representing one example of an aggregate III-nitride crystal substrate employed in the manufacture of a freestanding III-nitride single-crystal substrate involving the present invention.

FIG. 7 is a plan view summarily representing another example of a freestanding III-nitride single-crystal substrate involving the present invention.

FIG. 8 is a plan view summarily representing still another example of a freestanding III-nitride single-crystal substrate involving the present invention.

FIG. 9 is a schematic diagram representing one example of an apparatus, utilized in the present invention, for liquid-phase deposition of III-nitride crystal.

FIG. 10 is a schematic diagram representing one example of an apparatus, utilized in the present invention, for vapor-phase deposition of III-nitride crystal.

FIG. 11 is a sectional diagram summarily illustrating one example of a semiconductor device substrate prepared in a semiconductor device manufacturing method involving the present invention.

FIG. 12 is a sectional diagrams summarily illustrating another example of a semiconductor device substrate prepared in the semiconductor device manufacturing method involving the present invention.

FIG. 13 is a sectional diagram summarily representing one example of a process step whereby semiconductor devices are obtained in a semiconductor device manufacturing method involving the present invention.

FIG. 14 is a sectional diagram summarily illustrating one example of a process step of segmenting the semiconductor devices into chips in the semiconductor device manufacturing method involving the present invention.

FIG. 15 is a sectional diagram summarily illustrating one example of a semiconductor device chip obtained by the semiconductor device manufacturing method involving the present invention.

DETAILED DESCRIPTION OF THE INVENTION Embodying Mode 1 Freestanding III-Nitride Single-Crystal Substrate

Reference is made to FIGS. 1, 2, 7 and 8: With a freestanding III-nitride single-crystal substrate 20 p that is one mode of embodying the present invention, the average dislocation density is 5×10⁵ cm⁻² or less. The dislocation density in the substrate is found by measuring the density of dark spots under cathodoluminescence (CL), or by etching the substrate and measuring the density of etch-pits thereby produced in its major surface. In the present embodying mode, the dislocation density of the substrate is found from dark-spot density measurements by CL. Herein, “average dislocation density” means the average density of dark spots measured by CL globally across the substrate major surface (that is, across the entire major surface of later-described high-dislocation-density regions and low-dislocation-density regions).

A further characteristic of the present freestanding III-nitride single-crystal substrate 20 p is that it includes one or more high-dislocation-density regions 20 h, and a plurality of low-dislocation-density regions 20 k where the dislocation density is lower than that of the high-dislocation-density regions 20 h. The fact that the present freestanding III-nitride single-crystal substrate 20 p includes the high-dislocation-density regions 20 h and low-dislocation-density regions 20 k, makes it possible to arrest the propagation of cracks arising in the substrate, making it possible to prevent fracturing of the substrate.

In particular, with the present freestanding III-nitride single-crystal substrate 20 p, the ratio of the dislocation density of the high-dislocation-density region(s) 20 h to the dislocation density of the low-dislocation-density regions 20 k is sufficiently large to check the propagation of cracks in the substrate, and thus the ratio of the dislocation density of the high-dislocation-density region(s) 20 h to the average dislocation density is sufficiently large to check the propagation of cracks in the substrate. By having the dislocation-density distribution in the substrate be non-uniform, to make the ratio of the dislocation density of the high-dislocation-density region(s) 20 h to the average dislocation density sufficiently large, the propagation of cracks arising in the substrate can be arrested, enabling fracturing of the substrate to be prevented.

Herein, in respect of the ratio of the dislocation density of the high-dislocation-density region(s) 20 h to the average dislocation density, the size sufficient to arrest the propagation of cracks will differ depending on the crystalline structure and chemical composition of the substrate. With freestanding III-nitride single crystal substrates in which the substrate is of the hexagonal crystal system—for example, GaN single-crystal freestanding substrates, AlN single-crystal freestanding substrates, InN single-crystal freestanding substrates, Al_(x)Ga_(1-x)N (0<x<1) single-crystal freestanding substrates, and In_(y)Ga_(1-y)N (0<y<1) single-crystal freestanding substrates—the ratio of the dislocation density of the high-dislocation-density region(s) 20 h to the average dislocation density is preferably 2 or greater, more preferably 5 or greater, still more preferably 10 or greater. “Dislocation density of the high-dislocation-density region(s) 20 h” herein means the average density of dark spots quantified by the CL method over the major surface of the high-dislocation-density region(s).

The present freestanding III-nitride single-crystal substrate 20 p, furthermore, is not particularly limited, so long as the average dislocation density is 5×10⁵ cm⁻² or less and the ratio of the dislocation density of the high-dislocation-density region(s) 20 h to the average dislocation density is sufficiently large to check the propagation of cracks in the substrate, but from the perspective of managing both to prevent fracturing of the substrate and to prevent detriment to the properties of semiconductor devices obtained by forming an at least single-lamina III-nitride semiconductor layer onto the substrate, the dislocation density of the high-dislocation-density region(s) 20 h preferably is between 5×10⁵ cm⁻² and 3×10⁶ cm⁻², more preferably between 5×10⁵ cm⁻² and 2×10⁶ cm⁻², still more preferably between 5×10⁵ cm⁻² and 1×10⁶ cm⁻². And from the perspective of reducing the dislocation density of the low-dislocation-density regions 20 k to reduce the average dislocation density, the dislocation density of the low-dislocation-density regions 20 k is preferably 1×10⁵ cm⁻² or less, more preferably 1×10⁴ cm⁻² or less, still more preferably 1×10³ cm⁻² or less. “Dislocation density of the low-dislocation-density region(s) 20 k” herein means the average density of dark spots quantified by the CL method over the major surface of the low-dislocation-density regions 20 k.

Reference is again made to FIGS. 1, 2, 7 and 8: It is preferable that the present freestanding III-nitride single-crystal substrate 20 p have a hexagonal crystal-system structure, and that any chosen {1-100} plane 20 c in the substrate intersect the one or more high-dislocation-density regions 20 h. A freestanding III-nitride single crystal substrate having a hexagonal crystal-system structure has as the cleavage planes, which are most liable to fracture, the {1-100} planes 20 c. Thus, on account of the {1-100} planes 20 c intersecting the one or more high-dislocation-density regions 20 h, the propagation of cracks along the {1-100} planes 20 c is arrested. Fracturing of the substrate can thereby be efficiently prevented.

The reason herein is: Supposing, for example with reference to FIG. 1, that any chosen {1-100} plane 20 c does not include a {1-100} plane 20 d that is present only on the peripheral edge of the substrate. It could be that such a {1-100} plane 20 d does not intersect the high-dislocation-density region(s) 20 h. Nevertheless, even if there is a {1-100} plane 20 d that is present only on the peripheral edge of the substrate, it will not be a problem, in that it will not lead to the substrate thereby fracturing.

With reference yet again to FIGS. 1, 2, 7 and 8, the one or more high-dislocation-density regions 20 h in the present freestanding III-nitride single-crystal substrate 20 p are patterned in a geometry, seen from the major surface of the substrate, that preferably includes any of striped patterns (cf. FIG. 1), polygonally checkered patterns (cf. FIG. 2), periodically arrayed islet patterns (cf. FIG. 7), or nonrepetitive patterns (cf. FIG. 8). That the one or more high-dislocation-density regions 20 h are patterned in a geometry, seen from the major surface of the substrate, that includes any of striped patterns (cf. FIG. 1), polygonally checkered patterns (cf. FIG. 2), periodically arrayed islet patterns (cf. FIG. 7), or nonrepetitive patterns (cf. FIG. 8) makes it so that the {1-100} planes 20 c can intersect even more of the high-dislocation-density regions 20 h, thanks to which fracturing of the substrate can be more efficiently prevented.

Herein, in FIG. 2, an instance in which the polygonally checkered pattern is a square-check pattern is registered, but the polygonal form constituting the polygonally checkered pattern may be, other than square, triangular, rectangular, rhomboid, parallelogrammic, trapezoidal, hexagonal, etc. Likewise, it is sufficient for the periodically arrayed islet pattern form or nonrepetitive pattern form, as depicted in FIG. 7 and FIG. 8, of the high-dislocation-density regions 20 h, to be geometries whereby any chosen {1-100} plane 20 c intersects the one or more high-dislocation-density regions 20 h; the high-dislocation-density regions 20 h do not have to be continuous, and the positional relationships between each high-dislocation-density region 20 h separate from another are not limited to the positional relationships depicted in FIG. 7 or FIG. 8.

Freestanding III-Nitride Single Crystal Substrate Manufacturing Methods

While the method of manufacturing a freestanding III-nitride single crystal substrate of the present embodying mode is not particularly limited, the following two manufacturing methods are given as examples.

First Manufacturing Method

With reference to FIGS. 3 and 4, the first manufacturing method includes: a step (FIG. 3A and FIG. 4) of preparing a starting substrate 1 constituted by III-nitride crystal having matrices 1 s, and inversion domains 1 t in which the polarity in the <0001> directions is inverted with respect to that of the matrices 1 s; a step (FIG. 3B) of growing III-nitride crystal 10 by liquid-phase deposition onto the matrices 1 s and inversion domains 1 t in the starting substrate 1; a step (FIG. 3C) of growing III-nitride single crystal 20 by vapor-phase deposition onto the III-nitride crystal 10; and a step (FIGS. 3C and 3D) of processing the III-nitride single crystal 20 to form a freestanding III-nitride single crystal substrate 20 p. Herein, FIG. 3A is an outline section diagram along IIIA-IIIA in FIG. 4, while FIG. 3D is an outline section diagram along IIID-IIID in FIG. 1.

For the step of preparing the starting substrate 1, referring to FIG. 3A and FIG. 4, such a starting substrate 1 is manufactured by a facet-growth method based on hydride vapor-phase epitaxy (HVPE)—for example, as described in paragraphs [0221] through [0271] of Japanese Unexamined Pat. App. Pub. No. 2003-183100. The dislocation density of the matrices 1 s of the starting substrate 1 will be low, while the dislocation density of the inversion domains 1 t in the starting substrate 1 will, compared with that of the matrices 1 s, be high.

In the step, referring to FIG. 3B, of growing the III-nitride crystal 10 by liquid-phase deposition, first zones 10 s of the III-nitride crystal 10 grown onto the matrices 1 s of the starting substrate 1 grow as crystal inheriting the polarity and low-density dislocations of the matrices 1 s. Likewise, second zones 10 t of the III-nitride crystal 10 grown onto the inversion domains 1 t in the starting substrate 1 grow as crystal inheriting the polarity and high-density dislocations of the inversion domains 1 t. Consequently, the <0001> oriented polarity of the second zones 10 t of the III-nitride crystal 10 is inverted with respect to that of the first zones 10 s, while the dislocation density is higher. Herein, the liquid-phase deposition method is not particularly limited, but from the perspective of epitaxially growing III-nitride crystal whose dislocation density is low, Na flux growth is preferred.

Yet the crystal growth rate in the first zones 10 s is greater than the crystal growth rate in the second zones 10 t. Therefore, as the III-nitride crystal 10 grows, the first zones 10 s cover and bury over the second zones 10 t. In this way growing the III-nitride crystal 10 leaves only the first zones 10 s present at and over a certain crystal thickness, whereby at least the surface has a singular polarity. In the first zones 10 s grown thus, low-dislocation-density regions 10 k, where the crystal grows onto the matrices 1 s of the starting substrate 1, and high-dislocation-density regions 10 h, where the crystal grows onto the buried second zones 10 t are included. Depending on the pitch P and width W dimensions of the inversion domains in the starting substrate 1, however, in some instances high-dislocation-density regions 10 h will not be contained in the first zones 10 s.

Herein, with reference to FIGS. 3A and 3B and FIG. 4, in order to produce high-dislocation-density regions 10 h in the first zones 10 s of the III-nitride crystal 10 grown by liquid-phase deposition, it is preferable to have the pitch P of the inversion domains 1 t of the starting substrate 1 be 0.1 to 30 mm, and the width W thereof be 0.01 to 0.1 mm. By the same token, in order not to produce high-dislocation-density regions 10 h in the first zones 10 s of the III-nitride crystal 10 grown by liquid-phase deposition, it is preferable to have the pitch P of the inversion domains 1 t of the starting substrate 1 be 0.01 to 0.1 mm, and the width W thereof be 0.0001 to 0.01 mm.

In the step, referring to FIG. 3C, of growing the III-nitride single crystal 20 by vapor-phase deposition, the III-nitride single crystal 20 grown onto the III-nitride crystal 10 includes low-dislocation-density regions 20 k where the crystal grows onto the low-dislocation-density regions 10 k in the first zones 10 s of the III-nitride crystal 10, inheriting the zones' low-density dislocations, and high-dislocation-density regions 20 h where the crystal grows onto the high-dislocation-density regions 10 h in the first zones 10 s of the III-nitride crystal 10, inheriting the zones' high-density dislocations. Herein, the vapor-phase deposition method is not particularly limited, but from the perspective of epitaxially growing crystal of high dislocation density at an advanced rate, HVPE (hydride vapor-phase epitaxy) is preferred.

In the step, referring to FIGS. 3C and 3D, of processing the III-nitride single crystal 20 to form a freestanding III-nitride single crystal substrate 20 p, the III-nitride single crystal 20 grown by vapor-phase deposition is sliced along planes 20 u and 20 v parallel to the major surface of the starting substrate 1, after which the cut sides are polished to yield a freestanding III-nitride single crystal substrate 20 p having major surfaces 20 m and 20 n. Herein, in order to render the freestanding III-nitride single crystal substrate 20 p, the substrate thickness is preferably 100 μm or greater, more preferably 200 μm or greater, still more preferably 300 μm or greater.

Second Manufacturing Method

With reference to FIGS. 5 and 6, the second manufacturing method includes: a step (FIGS. 5A and 6) of arranging a plurality of III-nitride crystal chip substrates 11 a and 11 b so that their major surfaces parallel each other, and so that their lateral sides adjoin each other, to form a III-nitride crystal aggregate substrate 11; a step (FIG. 5B) of growing III-nitride single crystal 20 by vapor-phase deposition onto the major surface of the III-nitride crystal aggregate substrate 11; and a step (FIGS. 5B and 5C) of processing the III-nitride single crystal 20 to form a freestanding III-nitride single crystal substrate 20 p. Herein, FIG. 5A is an outline section diagram along VA-VA in FIG. 6, while FIG. 5C is an outline section diagram along VC-VC in FIG. 2.

Referring to FIGS. 5 and 6, the geometry of the major surfaces of the III-nitride crystal chip substrates 11 a and 11 b utilized in the step of forming the III-nitride crystal aggregate substrate 11 is not particularly limited, but from the viewpoint of tiling over, without gaps, any given planar surface, a triangular, quadrangular or hexagonal geometry is preferable, while an equilateral-triangular, square, rectangular, rhomboid, parallelogrammic, trapezoidal or regular-hexagonal geometry is more preferable.

In the present method, it is preferable that the plane orientations of the major surfaces of the plurality of III-nitride crystal chip substrates 11 a and 11 b be, from the standpoint of growing III-nitride single crystal 20 of superior crystallinity, identical or almost identical. On the other hand, in order to increase the dislocation density of the high-dislocation-density regions 20 h that grow over the plane of contiguity lie between the III-nitride crystal chip substrates 11 a and 11 b, to enhance the cracking-prevention effectiveness, the plane orientations of the major surfaces of the plural III-nitride crystal chip substrates 11 a and 11 b preferably are minutely displaced from each other. The direction of the plane-orientation displacement may be along a tilt line (direction slanted with respect to the c-axis of the III-nitride crystal) or may be along a twist line (direction skewed around the c-axis of the III-nitride crystal).

For the III-nitride crystal aggregate substrate 11 as a whole, however, because large displacement of the plane orientation of the major surfaces would be undesirable, the III-nitride crystal chip substrates 11 a and 11 b are more preferably arranged so that the directions of the plane-orientation displacement of the major surfaces of the adjoining III-nitride crystal chip substrates 11 a and 11 b will be such that the displacements cancel each other out. For example, referring to FIG. 5A, III-nitride crystal chip substrate 11 a with major surface having plane orientation in direction A, and III-nitride crystal chip substrate 11 b with major surface having plane orientation in direction B are disposed with the directions of the plane-orientation displacement of the major surfaces of the adjoining III-nitride crystal chip substrates 11 a and 11 b being such that the displacements cancel each other out.

In the step, referring to FIG. 5B, of growing the III-nitride single crystal 20 by vapor-phase deposition, the III-nitride single crystal 20 grown onto the III-nitride crystal aggregate substrate 11 includes low-dislocation-density regions 20 k where the crystal grows onto the respective major surfaces of the III-nitride crystal chip substrates 11 a and 11 b of the III-nitride crystal aggregate substrate 11, and high-dislocation-density regions 20 h where the crystal grows over the contiguity plane 11 e between the III-nitride crystal chip substrates 11 a and 11 b where they adjoin each other. Herein, the vapor-phase deposition method is not particularly limited, but from the perspective of epitaxially growing crystal of high dislocation density at an advanced rate, HVPE (hydride vapor-phase epitaxy) is preferred.

In the step, referring to FIGS. 5B and 5C, of processing the III-nitride single crystal 20 to form a freestanding III-nitride single crystal substrate 20 p, the III-nitride single crystal 20 grown by vapor-phase deposition is sliced along planes 20 u and 20 v parallel to the major surface of the III-nitride crystal aggregate substrate 11, after which the cut sides are polished to yield a freestanding III-nitride single crystal substrate 20 p having major surfaces 20 m and 20 n. Herein, in order to render the freestanding III-nitride single crystal substrate 20 p, the substrate thickness is preferably 100 μm or greater, more preferably 200 μm or greater, still more preferably 300 μm or greater.

Embodying Mode 2 Semiconductor Device Manufacturing Method

Reference is made to FIGS. 11 through 15: A semiconductor device 90 manufacturing method that is another mode of embodying the present invention is a method of manufacturing a semiconductor device 90 utilizing a freestanding III-nitride single crystal substrate 20 p of Embodying Mode 1, and specifically is provided with a step of utilizing the freestanding III-nitride single crystal substrate 20 p to prepare a semiconductor device substrate 90 p, and step of forming an at least single-lamina III-nitride semiconductor layer 70 onto the semiconductor device substrate 90 p.

In accordance with a semiconductor device manufacturing method in the present embodying mode, the semiconductor device substrate 90 p prepared utilizing the freestanding III-nitride single crystal substrate 20 p comprises III-nitride single crystal 20 in which the average dislocation density is not greater than 5×10⁵ cm⁻², including one or more high-dislocation-density regions 20 h and a plurality of low-dislocation-density regions 20 k in which the dislocation density is lower than that of the high-dislocation-density region(s) 20 h. Manufacture therefore without giving rise to fractures in the semiconductor device substrate 90 p enables the production at high yield rates of semiconductor devices with superior device properties.

Semiconductor Device Substrate Preparation Step

While the method of preparing the semiconductor device substrate 90 p, referring to FIGS. 11 and 12, is not particularly limited as long as the substrate that is prepared comprises III-nitride single crystal 20, having one major surface 90 m, of average dislocation density not greater than 5×10⁵ cm⁻² and including one or more high-dislocation-density regions 20 h and a plurality of low-dislocation-density regions 20 k in which the dislocation density is lower than that of the high-dislocation-density region(s) 20 h, the following method is given as an example.

For the semiconductor device substrate 90 p, referring to FIG. 11, a freestanding III-nitride single crystal substrate 20 p of Embodying Mode 1 may be prepared. While the method of preparing the freestanding III-nitride single crystal substrate 20 p of Embodying Mode 1 is not particularly limited, the First Manufacturing Method or the Second Manufacturing Method in the freestanding III-nitride single crystal substrate manufacturing methods of Embodying Mode 1 can be utilized.

Alternatively, for the semiconductor device substrate 90 p, referring to FIG. 12, a template substrate may be prepared in which are bonded a III-nitride single crystal 20 q that is the product of thinning down to a film a freestanding III-nitride single crystal substrate 20 p, and a heterosubstrate 90 pb whose chemical composition differs from that of the III-nitride single crystal 20.

With reference to FIG. 12, the afore-described template substrate can be prepared in the following way. To begin with, a freestanding III-nitride single crystal substrate 20 p, referring to FIG. 12A, is prepared.

Next, referring to FIG. 12B, the heterosubstrate 90 pb is bonded to the major surface of the freestanding III-nitride single crystal substrate 20 p. Herein, the heterosubstrate 90 pb is not particularly limited as long as it is a material capable of bonding with the freestanding III-nitride single crystal substrate 20 p, and substrates having durability suited to the manufacture of the target semiconductor devices can be selected. Materials that may be cited given such considerations include: III-nitride substrates whose chemical composition differs from that of the III-nitride single crystal 20; sapphire substrates; SiC substrates; Si substrates; ZnSe substrates; ZnO substrates; ZnS substrates; MgO substrates; quartz substrates; carbon substrates; diamond substrates; Ga₂O₃ substrates; and ZrB substrates. And while the method of bonding the heterosubstrate 90 pb is not particularly limited, from the perspective of enabling uniform bonding at low temperatures, methods such as surface-activated bonding and fusion bonding are preferable. Herein, “surface-activated bonding” means a technique whereby the surfaces to be bonded are bombarded with a plasma to superficially active them, and then the surfaces are joined together, while “fusion bonding” means a technique of applying pressure and heat to cleaned mating surfaces to be bonded, and joining the surfaces together.

Next, referring to FIGS. 12B and 12C, the freestanding III-nitride single crystal substrate 20 p is divided along a plane that is a predetermined distance T (for example, between 0.01 μm and 100 μm) from the single-crystal substrate's interface with the heterosubstrate 90 pb. The method of dividing the freestanding III-nitride single crystal substrate 20 p is not particularly limited, and methods employing devices such as electric-discharge machines, wire saws, dicing saws, internal diameter saws, and laser saws can be cited. Alternatively, while not illustrated in the figures, it is also possible to implant ions into a region of the freestanding III-nitride single crystal substrate that is alongside the surface that bonds the heterosubstrate and which has a predetermined depth T from that surface, thereafter bond on the heterosubstrate, and, by means of heat, force, etc., apply stress to the single-crystal substrate to divide it along the ion-implanted region. In that case, hydrogen ions, helium ions, etc. are employed as the implantation ions. Dividing the freestanding III-nitride single crystal substrate 20 p, bonded to the heterosubstrate 90 pb, along a plane at a predetermined distance T from its interface with the heterosubstrate 90 pb removes remainder III-nitride single crystal substrate 20 r from the freestanding III-nitride single crystal substrate 20 p, to form a III-nitride single crystal layer 20 q of thickness T, bonded to the heterosubstrate 90 pb. In this way, as a semiconductor device substrate 90 p, a template substrate including the heterosubstrate 90 pb and, formed onto the heterosubstrate 90 pb as a III-nitride seed crystal layer 90 pa, the III-nitride single crystal layer 20 q of thickness T is obtained.

Step of Forming Minimally Single-Lamina III-Nitride Semiconductor Layer

Reference is made to FIG. 13: Onto a one major surface 90 m of the semiconductor device substrate 90 p, an n⁺-type GaN layer 72, an n-type GaN layer 74, and a p-type GaN layer 76, for example, are formed as an at least single-lamina III-nitride semiconductor layer 70. In this way a p-n junction plane 90 ^(j) is formed in between the p-type GaN layer 76 and the n-type GaN layer 74. Herein, the one major surface 90 m corresponds in the semiconductor device substrate 90 p to the freestanding III-nitride single crystal substrate 20 p (cf. FIG. 11), or to the major surface 20 m of the III-nitride single crystal layer 20 q. And while the method of forming the at least single-lamina III-nitride semiconductor layer 70 is not particularly limited, from the perspective of epitaxially growing low-dislocation-density, superior-crystallinity semiconductor layers, vapor deposition methods such as metalorganic chemical vapor deposition (MOCVD), hydride vapor-phase epitaxy (HVPE), molecular-beam epitaxy (MBE), and sublimation growth are preferably utilized.

Next, an Ni/Au laminate electrode is formed, as a p-side electrode 82, onto the p-type GaN layer 76 (with the Ni layer in contact with the p-type GaN layer), and a Ti/Al laminate electrode is formed, as an n-side electrode 84, onto the other major surface 90 n of the semiconductor device substrate 90 p (with the Ti layer in contact with the semiconductor device substrate 90 p), yielding a semiconductor device 90. Herein, while the method of forming the p-side electrode 82 and n-side electrode 84 is not particularly limited, from a high productivity standpoint, such methods as evaporation deposition and sputter deposition are preferable.

Further, referring to FIG. 14, the p-side electrode 82, p-type GaN layer 76, and a portion of the n-type GaN layer 74 are mesa-etched along dicing streets 90 d in the just-described semiconductor device 90. Subsequently, by segmenting the semiconductor device 90 along the dicing streets 90 d, semiconductor device chips 90 c are obtained. By segmenting a single semiconductor device 90 into ten chips C1 through C10, for example, ten semiconductor device chips 90 c are produced.

Embodiments

1. Manufacture of Freestanding GaN Single-Crystal Substrates (Freestanding III-Nitride Single Crystal Substrates)

In the present embodiment, freestanding GaN single crystal substrates (freestanding III-nitride single crystal substrates) were produced in the following manner, according to the above-described First Manufacturing Method.

1-1. Preparation of GaN Starting Substrates Having Matrices and Inversion Domains

Reference is made to FIG. 3A and FIG. 4: 2-inch (5.08 cm) diameter, 350-μm thick starting substrates 1 of GaN crystal (termed GaN starting substrates 1 hereinafter) were prepared, having a plurality of matrices 1 s in which the dislocation density was 0.1 to 1×10⁵ cm⁻², and a plurality of inversion domains 1 t in which the dislocation density was 0.1 to 1×10^(9 cm) ⁻². Along one major surface of the GaN starting substrates 1, the (0001) surface (Ga-atom surface) of the matrices 1 s appeared, while the (000-1) surface (N-atom surface) of the inversion domains 1 t appeared. Furthermore, the inversion domains 1 t extended from one edge to the other edge of the starting substrates 1, along their <1-100> directions in a striped formation. Here, sample GaN starting substrates 1 of two kinds were prepared: Starting Substrates A, in which the pitch P of the inversion domains 1 t was 1 mm and the width W thereof was 0.01 mm; and Starting Substrates B, in which the pitch of the inversion domains 1 t was 0.05 mm and the width was 0.01 mm.

1-2. Growth of GaN Crystal (III-Nitride Crystal) by Na Flux Growth (Liquid-Phase Deposition)

With reference to FIG. 3B and FIG. 9, GaN crystal (III-nitride crystal 10) was grown in the following manner by the Na flux method onto the two types of GaN starting substrate 1 just described—Starting Substrates A and Starting Substrates B.

Referring to FIG. 9, a crystal-growth reactor employed in growing the III-nitride crystal by the Na-flux method is furnished with, for example: an outer chamber 39; a thermally insulating component 37 disposed in the inside of the outer chamber 39; a heater 35 disposed in the inside of the insulating component 37; and an inner chamber 31 disposed inward of the heater 35. A crystal-growth vessel 33 for growing within it the III-nitride crystal 10 is disposed inside the inner chamber 31. Further, the opening in the crystal-growth vessel 33 may be covered by a lid 34. Herein, while the material of the crystal-growth vessel 33 and the lid 34 is not particularly limited as long as it does not react with solvent 3 and nitrogen-containing gas 5, and is of high mechanical strength and heat resistance, a material such as BN (boron nitride) is preferable. And while the material of the inner chamber 31 is not particularly limited as long as it is of high mechanical strength and heat resistance, materials such as stainless and heat-resistant steels are preferable. Likewise, while the material of the outer chamber 39 is not particularly limited as long as it is of high mechanical strength and heat resistance, materials such as stainless steels are preferable. And while the material of the thermally insulating component 37 is not particularly limited as long as it is of high mechanical strength, heat resistance, and insulating ability, materials such as graphite wool are preferable.

The present crystal-growth reactor is also provided with: a nitrogen-containing-gas supply device 41 connected to the inner chamber 31 by a first supply line 51; a pressurizing gas supply device 43 connected to the outer chamber 39 by a second supply line 53; and a evacuation pump 45 connected to the outer chamber 39 by a third supply line 55. The first supply line 51 herein is furnished with a valve 51 v for adjusting the supply flow volume of the nitrogen-containing gas 5, while the supply-line section 51 a to the inner chamber 31 side of the valve 51 v is provided with a first pressure gauge 51 p. Likewise, the second supply line 53 is furnished with a valve 53 v for adjusting the supply flow volume of the pressurizing gas 7, while the supply-line section 53 a to the outer chamber 39 side of the valve 53 v is provided with a second pressure gauge 53 p. Furthermore, the third supply line 55 is furnished with a valve 55 v for adjusting the exhaust flow volume.

The growth reactor is additionally provided with a fourth supply line 57 connecting the section 51 a of the first supply line 51 to the inner chamber 31 side of valve 51 v with the section 55 a of the third supply line 55 to the outer chamber 39 side of valve 55 v. The fourth supply line 57 is provided with a valve 57 v. It will be appreciated that in FIG. 9, for the sake of reference, the section 51 b of the first supply line 51 to the nitrogen-containing-gas supply device 41 side of valve 51 v, the section 53 b of the second supply line 53 to the pressurizing-gas supplying device 43 side of valve 53 v, and the section 55 b of the third supply line 55 to the evacuation-pump 45 side of valve 55 v are also illustrated.

Referring to FIG. 9, the above-described GaN starting substrate 1 of the two types were each placed on the bottom of a boron-nitride crucible (crystal-growth vessel 33) of 60 mm inner diameter and 20 mm depth, with the aforementioned one major surface facing up (substrate placement substep). Next, 15 g of metallic Ga of 99.9999 mol % purity, and 11 g of metallic Na (solvent 3) of 99.99 mol % purity were put into the BN crucible (crystal-growth vessel 33) into which the GaN starting substrates 1 had been placed (solvent placement substep). The metallic Ga and metallic Na (solvent 3), which are solid at room temperature (approximately 25° C.), by subsequent heating were liquefied into a metallic Ga—Na melt in which the molar ratio of metallic Ga (Group-III metal M_(III)) to metallic Na (alkali metal M_(A)) M_(III):M_(A)=31:69, with the depth from the surface of the metallic Ga—Na melt (solvent 3) to the major surface of the GaN starting substrates 1 being 5 mm.

Next, the BN crucible (crystal-growth vessel 33) in which the GaN starting substrates, as well as the metallic Ga and metallic Na (solvent 3), had been contained was set inside the inner chamber 31. A boron-nitride lid 34 was placed on top of the BN crucible (crystal-growth vessel 33)—(crystal-growth container placement substep).

Next, a vacuum pump (the evacuation pump 45) was employed to evacuate the interior of the inner chamber 31 and outer chamber 39 (evacuation substep). The vacuum level in the inner chamber 31 and outer chamber 39 following evacuation was 1×10⁻³ Pa.

Nitrogen-containing gas 5 and pressurizing gas 7 were then respectively supplied into interior of the inner chamber 31 and outer chamber 39 so that the internal pressure of each chamber would be 1 MPa (nitrogen-containing gas supply substep). In this process, a high-purity nitrogen gas of 99.99999 mol % purity was used for the nitrogen-containing gas 5 supplied inside the inner chamber 31. Meanwhile, nitrogen gas of 99.9999 mol % purity was used for the pressurizing gas 7 supplied to the outer chamber 39.

Next, the heater 35, which was of the resistive heating type, was employed to heat the inside of the inner chamber 31 and outer chamber 39, and bring the temperature of the inner chamber 31 interior overall to 870° C. (heating substep). This heating liquefied the metallic Ga and metallic Na (solvent 3) placed in the inner chamber 31, covering the aforementioned major surface of the GaN starting substrates 1 and dissolving the high-purity nitrogen gas (nitrogen-containing gas 5) into the liquefied metallic Ga and metallic Na, i.e., the Ga—Na melt (solvent 3). In this way, it was possible to bring the solution in which the high-purity nitrogen gas (nitrogen-containing gas 5) was dissolved into the Ga—Na melt (solvent 3) into contact with the said one major surface of the GaN substrates (starting substrates 1). During the heating, high-purity nitrogen gas (nitrogen-containing gas 5) was additionally supplied to the inner chamber 31 to make the internal pressure of the inner chamber 31 in the range of from 0.01 MPa to 0.1 MPa greater than that of the internal pressure of the outer chamber 39. That is, the pressure situation was made so that 0.01 MPa≦{(inner-chamber internal pressure)-(outer-chamber internal pressure)}≦0.1 MPa.

Subsequently, the amount of the nitrogen-containing gas 5 supplied, and the amount of heat added, to the inner chamber 31 were adjusted to bring the internal pressure of the inner chamber 31 to 3 MPa (crystal-growth pressure) with the temperature of the inner chamber 31 interior overall being kept at 870° C. (crystal-growth temperature), and GaN crystal (III nitride crystal 10) was grown onto the said major surface of the GaN starting substrates 1 for 200 hours (crystal-growth substep). In this process, the amount of the nitrogen gas (pressurizing gas 7) supplied to the outer chamber 39 was adjusted to make the internal pressure of the outer chamber 39 in the range of from 0.01 MPa to 0.1 MPa less than that of the internal pressure of the inner chamber 31. That is, likewise as during heating, during crystal growth the pressure situation was made so that 0.01 MPa≦{(inner-chamber internal pressure)-(outer-chamber internal pressure)}≦0.1 MPa.

Next, the interiors of both the inner chamber 31 and the outer chamber 39 were cooled and depressurized, with the relationship 0.01 MPa≦{(inner-chamber internal pressure)-(outer-chamber internal pressure)}≦0.1 MPa being maintained, and from the Ga—Na melt (solvent 3) in the BN crucible (crystal-growth vessel 33) within the inner chamber 31 having been cooled to 30° C., the GaN crystal (III nitride crystal 10) grown onto the GaN starting substrates 1 was taken out with tweezers. The thickness of the obtained GaN crystal was 200 μm. That meant that the GaN crystal-growth rate was 1 μm/hr.

In the above-described way, GaN crystal A (III-nitride crystal 10) produced on Starting Substrates A (starting substrates 1) contained low-dislocation-density regions 10 k, grown onto the matrices 1 s in the Starting Substrates A, and high-dislocation-density regions 10 h, grown onto the buried second zones 10 t, and had an average dislocation density of 5×10⁵ cm⁻², with the dislocation density of the low-dislocation-density regions being 2 to 10×10⁴ cm⁻² and the dislocation density of the high-dislocation-density regions being 1 to 2×10⁶ cm⁻². Meanwhile, GaN crystal B (III-nitride crystal 10) produced on Starting Substrates B (starting substrates 1) formed essentially with low-dislocation-density regions 10 k only, grown onto the matrices 1 s in the Starting Substrates B, and had an average dislocation density of 2×10⁶ cm⁻², with an essentially uniform dislocation-density profile, in that the dislocation density of the low-dislocation-density regions was within a 1.5 to 2.5×10⁶ cm⁻² range. In the present application, a substrate's dislocation-density profile being “essentially uniform” means that in that substrate, the ratio of the dislocation density of the high-dislocation-density regions to the average dislocation density is less than 2, for example.

Herein, the dislocation density (dark-spot density under CL) of the substrates was calculated by determining the number of dark spots per unit area (surface area of a 100 μm×100 μm square region) where the substrate major surface was measured by CL, in 500 locations on points of a 100-μm pitch grid where the major surface intersected the high-dislocation-density regions perpendicular to their longitudinal direction.

1-3. Growth of GaN Single Crystal (III-Nitride Single Crystal) by HVPE (Vapor-Phase Deposition)

With reference to FIG. 3C and FIG. 10, III-nitride single crystal 20 was grown in the following manner by HVPE onto the aforedescribed two types of GaN crystal (III-nitride crystal 10).

Reference is made to FIG. 10: In the crystal-growth reactor employed to grow the III-nitride crystal by HVPE, exemplarily a crystal holder 602 for retaining the GaN crystal (III-nitride crystal 10) is disposed inside a reaction chamber 601; and a Group III chloride gas synthesis chamber 603 for synthesizing Group III chloride gas 63 that is introduced into the reaction chamber 601, an HCl gas introduction line 605 for introducing HCl gas 61 into the III-chloride gas synthesis chamber 603, a nitrogen precursor gas introduction line 606 for introducing nitrogen precursor gas 66 into the reaction chamber 601, and an exhaust duct 607 for exhausting the post-reaction gases are installed in the reactor. In addition, a Group III metal boat 604 into which Group IIII metal 62 is stored is disposed in the III-chloride gas synthesis chamber 603. And installed surrounding the III-chloride gas synthesis chamber 603 and the reaction chamber 601, for heating both the Group III metal boat 604 and the GaN crystal (III-nitride crystal 10), are heaters 608, 609 and 610.

With reference to FIG. 10, the Ga chloride gas (Group III chloride gas 63) that is introduced into the reaction chamber 601 is synthesized to begin with. Specifically, the Ga boat (Group III metal boat 604) disposed inside the Ga chloride synthesis chamber (III-chloride gas synthesis chamber 603) is heated with heater 609 to 800° C., HCl gas is introduced inside the Ga chloride synthesis chamber (III-chloride gas synthesis chamber 603) via the HCl gas introduction line 605, and the HCl gas 61 and the Ga (III-nitride metal 62) inside the Ga boat (Group III metal boat 604) are reacted to synthesize Ga chloride gas (Group III chloride gas 63). The HCl gas 61 in this case is introduced into the Ga chloride synthesis chamber (III-chloride gas synthesis chamber 603) together with a carrier gas such as H₂.

The Ga chloride gas (Group III chloride gas 63) just described and NH₃ gas (nitrogen precursor gas 66) were introduced into the reaction chamber 601 together with the H₂ gas as a carrier gas, and the Ga chloride gas (Group III chloride gas 63) and NH₃ gas (nitrogen precursor gas 66) were reacted over the GaN crystal (III-nitride crystal 10), placed atop the crystal holder 602 inside the reaction chamber 601 and heated to 110° C., whereby for 50 hours single-crystal GaN was grown, yielding a 10-mm thick GaN single-crystal.

In this process, in order to enhance uniformity in the amount of Ga chloride gas (Group III chloride gas 63) and NH₃ gas (nitrogen precursor gas 66) supplied to the major surface of the GaN substrate during growth of the GaN single crystal (III-nitride single crystal 20), the GaN crystal (III-nitride crystal 10) was disposed atop the crystal holder 602, slanted 100 with respect to the horizontal, and rotated at a turning rate of 60 rpm. Also, the partial pressure of the Ga chloride gas (Group III chloride gas 63) was made 5.065 kPa (0.05 atm), and the partial pressure of the NH₃ gas (nitrogen precursor gas 66), 10.13 kPa (0.1 atm).

In the above-described way, GaN single crystal A (III-nitride single crystal 20) produced on GaN crystal A (III-nitride crystal 10) contained low-dislocation-density regions 20 k, grown onto the matrices 1 s in the GaN starting substrates A, and high-dislocation-density regions 20 h, grown onto the buried second zones 10 t, and had an average dislocation density of 3×10⁵ cm⁻², with the dislocation density of the low-dislocation-density regions being 2 to 10×10⁴ cm⁻² and the dislocation density of the high-dislocation-density regions being 5 to 10×10⁵ cm ². Meanwhile, GaN single crystal B (III-nitride single crystal 20) produced on GaN crystal B (III-nitride crystal 10)—which was produced on GaN starting substrates B—formed essentially with low-dislocation-density regions 20 k only, grown onto the matrices 1 s in the GaN crystal B (III-nitride crystal 10), and had an average dislocation density of 3×10⁵ cm⁻², with an essentially uniform dislocation-density profile, in that the dislocation density of the low-dislocation-density regions was within a 2.5 to 3.8×10⁵ cm⁻² range.

1-4. Manufacture of Freestanding GaN Single-Crystal Substrates (Freestanding III-Nitride Single Crystal Substrates)

Referring to FIGS. 3C and 3D, the GaN single crystal (III-nitride single crystal 20) obtained in the manner described above was sliced along planes 20u and 20 v parallel to the major surface of the starting substrate 1, yielding freestanding GaN single crystal wafers (freestanding III-nitride single crystal wafers) of 500 μm thickness. Subsequently, chemical-mechanical polishing (CMP) was employed to process the major surface of the freestanding GaN single crystal wafers (freestanding III-nitride single crystal wafers) to a specular finish, yielding a plurality of 400-μm thick freestanding GaN single crystal substrates (freestanding III-nitride single crystal substrates 20 p).

2. Evaluation of Fracture Strength of Freestanding GaN Single-Crystal Substrates (Freestanding III-Nitride Single Crystal Substrates)

The plurality of freestanding GaN single crystal substrates just described was grouped into: ten substrates (Group 1) whose average dislocation density was in the range of 3 to 5×10⁵ cm⁻², dislocation density of the low-dislocation-density regions, 2 to 10×10⁴ cm⁻², and dislocation density of the high-dislocation-density regions, 10 to 20×10⁵ cm⁻²; ten substrates (Group 2) whose average dislocation density was 3 to 5×10⁵ cm⁻², and having an essentially uniform dislocation-density profile (the ratio of dislocation density of the high-dislocation-density regions to the average dislocation density was less than 2); and ten substrates (Group 3) whose average dislocation density was 10 to 20×10⁵ cm⁻², and having an essentially uniform dislocation-density profile. In the evaluation, the Group 1 substrates were taken as Embodiment I of the invention in the present application, while the Group 2 and Group 3 substrates were taken as Comparative Example II and Comparative Example III, respectively.

The ten freestanding GaN single crystal substrates of each group were each housed individually in a wafer tray of polypropylene for a single 2-inch wafer, and fixed with a spring. For each group of the manufactured substrates that had been housed in this way, the ten wafer trays were dropped in a freefall onto a concrete floor from a height of 50 cm. With the Group 1 substrates, among the ten there were none that fractured (Embodiments 1-1 through 1-10). With the Group 2 substrates, among the ten there were seven that fractured (Comparative Examples II-1 through II-10). With the Group 3 substrates, among the ten there were 2 that fractured (Comparative Examples III-1 through III-10). The results are tabulated in Tables I through III.

TABLE I High disloc. Total no. Dislocation density/ fractured Average density of low disloc. substrates, or dislocation high-dislocation density presence of density density regions dislocation individual Embod. I (×10⁵ cm⁻²) (×10⁵ cm⁻²) density ratio fractures Overall 3~5 10~20   2~6.7 0 substrates I-1 3.1 10~20 3.2~6.5 none I-2 3.5 10~20 2.9~5.7 none I-3 3.6 10~20 2.8~5.6 none I-4 3.8 10~20 2.6~5.3 none I-5 3.8 10~20 2.6~5.3 none I-6 3.9 10~20 2.6~5.1 none I-7 4.1 10~20 2.4~4.9 none I-8 4.3 10~20 2.3~4.7 none I-9 4.5 10~20 2.2~4.4 none I-10 4.6 10~20 2.2~4.3 none

TABLE II Total no. fractured Average substrates, or dislocation presence of density individual Comp. Ex. II (×10⁵ cm⁻²) fractures Overall 3~5 7 substrates II-1 3.3 present II-2 3.8 present II-3 3.9 present II-4 4.0 none II-5 4.2 present II-6 4.3 present II-7 4.4 present II-8 4.5 none II-9 4.5 present II-10 4.9 none

TABLE III Total no. fractured Average substrates, or dislocation presence of density individual Comp. Ex. III (×10⁵ cm⁻²) fractures Overall 10~20 2 substrates III-1 10 none III-2 12 none III-3 13 none III-4 13 present III-5 15 none III-6 15 none III-7 16 none III-8 18 none III-9 19 none III-10 20 present

As is clear from Table I, contrasting Comparative Example III with Comparative Example II evidences that among the freestanding III-nitride single crystal substrates in which the dislocation-density profile is essentially uniform, compared with substrates in which the average dislocation density is a large 10 to 20×10⁵ cm⁻², substrates in which the average dislocation density is a small 3 to 5×10⁵ cm⁻² are fracture-prone. Contrasting Comparative Example II with Embodiment I evidences that among the freestanding III-nitride single crystal substrates in which the average dislocation density is a small 3 to 5×10⁵ cm⁻², compared with substrates in which the dislocation-density profile is essentially uniform, substrates in which the dislocation-density profile is essentially non-uniform (in which ratio of the dislocation density of the high-dislocation-density regions to the average dislocation density is 2 or greater) are extremely unlikely to fracture.

3. Manufacture of Semiconductor Device

3-1. Semiconductor Device Substrate Preparation

Referring to FIG. 11, freestanding GaN single-crystal substrate I-10 (freestanding III-nitride single crystal substrate 20 p) obtained in Embodiment I-10 was prepared as a semiconductor device substrate 90 p.

3-2. Semiconductor Device Manufacture

Reference is made to FIG. 13: Onto a one major surface 90 m (referring to FIG. 11, the major surface 90 m corresponds to the major surface 20 m of the freestanding III-nitride single crystal substrate 20 p) of the freestanding GaN single-crystal substrate I-10 (semiconductor device substrate 90 p), by MOCVD a 0.6-μm thick n⁺-type GaN layer 72, a 7-μm thick n-type GaN layer 74 (electron density of 3×10¹⁶ cm⁻³), and a 0.5-μm thick p-type GaN layer 76 (Mg atom density of 7×10¹⁷ cm⁻³) were grown, in that order, as an at least single-lamina III-nitride semiconductor layer 70. In this way a p-n junction plane 90 j was formed in between the p-type GaN layer 76 and the n-type GaN layer 74. Next, an Ni layer and an Au layer were formed in that order as a p-side electrode 82, by evaporation deposition onto the p-type GaN layer 76 to create an Ni/Au laminate electrode. Then a Ti layer and an Al layer were formed in that order as an n-side electrode 84 by evaporation deposition onto the other major surface 90 n (referring to FIG. 11, the major surface 90 n corresponds to the major surface 20 n of the freestanding III-nitride single crystal substrate 20 p) of the freestanding GaN single-crystal substrate I-10 (semiconductor device substrate 90 p), creating a Ti/Al laminate electrode. In this way a semiconductor device 90 was produced.

Next, referring to FIGS. 14 and 15, the aforedescribed semiconductor device 90—the p-side electrode 82, p-type GaN layer 76, and a portion of the n-type GaN layer 74—was mesa-etched along its dicing streets 90 d. Subsequently, by segmenting the semiconductor device 90 along the dicing streets 90 d into ten chips C1 through C10 whose p-n junction plane 90 j size was 1 cm×1 cm, with no fractures arising in the semiconductor device 90, ten semiconductor device chips 90 c in which the p-n junction plane 90 j surface area was 1 cm² were obtained from the semiconductor device 90.

A reverse breakdown voltage test was conducted on the ten semiconductor device chips obtained, whereupon all ten semiconductor device chips had a reverse breakdown voltage of not less than 500 V, thus exhibiting exceedingly superior reverse breakdown voltage characteristics. Herein, a plurality of high-dislocation-density region 20 h were present in the freestanding GaN single-crystal substrate I-10 (freestanding III-nitride single crystal substrate 20 p) utilized as the semiconductor device substrate 90 p for the semiconductor device chips 90 c, extending along <1-100> directions in the substrate I-10, at a pitch of 1 mm along <11-20> directions in the substrate I-10. This means that the semiconductor device substrates 90 p in all of the semiconductor device chips 90 c contained a plurality of high-dislocation-density regions 20 h and low-dislocation-density regions 20 k. Accordingly, by utilizing a freestanding III-nitride single-crystal substrate in which the average dislocation density is not greater than 5×10⁵ cm⁻², and that includes one or more high-dislocation-density regions, and a plurality of low-dislocation-density regions in which the dislocation density is lower than that of the high-dislocation-density regions, semiconductor devices with enhanced device characteristics were obtained at high yields.

The presently disclosed embodying modes and embodiment examples should in all respects be considered to be illustrative and not limiting. The scope of the present invention is set forth not by the foregoing description but by the scope of the patent claims, and is intended to include meanings equivalent to the scope of the patent claims and all modifications within the scope.

A freestanding III-nitride single crystal substrate involving the present invention is utilized in applications including light-emitting devices such as light-emitting diodes and laser diodes, in electronic devices such as rectifiers, bipolar transistors, field-effect transistors, and high electron mobility transistors (HEMTs), semiconductor sensors such as temperature sensors, pressure sensors, radiation sensors, or visible-blind ultraviolet detectors, surface acoustic wave devices (SAW devices), vibrators, resonators, oscillators, microelectromechanical system (MEMS) parts, and piezoelectric actuators. 

1. A freestanding III-nitride single-crystal substrate in which the average dislocation density is not greater than 5×10⁵ cm⁻², including: one or more high-dislocation-density regions; and a plurality of low-dislocation-density regions in which the dislocation density is lower than that of said high-dislocation-density regions.
 2. A freestanding III-nitride single-crystal substrate as set forth in claim 1, wherein the ratio of the dislocation density of said high-dislocation-density region(s) to said average dislocation density is sufficiently large to check the propagation of cracks in said substrate.
 3. A freestanding III-nitride single-crystal substrate as set forth in claim 1, wherein the ratio of the dislocation density of said high dislocation density region(s) to said average dislocation density is 2 or greater.
 4. A freestanding III-nitride single-crystal substrate as set forth in claim 1, wherein the dislocation density of said high-dislocation-density region(s) is between 5×10⁵ cm⁻² and 3×10⁶ cm⁻².
 5. A freestanding III-nitride single-crystal substrate as set forth in claim 1, wherein the dislocation density of said low-dislocation-density regions is not greater than 1×10⁵ cm⁻².
 6. A freestanding III-nitride single-crystal substrate as set forth in claim 1, wherein: the substrate has a hexagonal crystal-system structure; and any chosen {1-100} plane in said substrate intersects said one or more high-dislocation-density regions.
 7. A freestanding III-nitride single-crystal substrate as set forth in claim 6, wherein: said one or more high-dislocation-density regions are patterned in a geometry, seen from the major surface of the substrate, that includes any of: striped patterns, polygonally checkered patterns, periodically arrayed islet patterns, or nonrepetitive patterns.
 8. A freestanding III-nitride single-crystal substrate as set forth in claim 1, wherein: the surface area of the substrate major surface is 20 cm² or greater; and the substrate thickness is 1000 μm or less.
 9. A freestanding III-nitride single-crystal substrate as set forth in claim 1, wherein the substrate is a GaN single-crystal freestanding substrate.
 10. A freestanding III-nitride single-crystal substrate as set forth in claim 1, wherein the substrate is formed by HVPE.
 11. A method of manufacturing a semiconductor device utilizing a freestanding III-nitride single-crystal substrate as set forth in claim
 1. 